Rotor parachute



Oct. 21, 1952 R. H. PREWITT 2,614,636

I ROTOR PARACHUTE Filed April 12, 1947 3 Sheets-Sheet l q. m K n d .6

Oct. 21, 1952 H. PREWITT 2,614,636

RoTbiz VPARACHUTE Filed April 12, 1947 3 Sheets-Sheet 2 \NVENTQR filchanL H- P e 4 (finale/n1- ATroRN i R. H. PREWITT ROTOR PARACHUTE Oct. 21, 1952 Filed April 12, 1947 5.Sheets-Sheet 3 III m R a v 2 M NM MR E o v m T m? M u. 4 W n m on Patented Oct. 21, 1952 UNITED STATES PATENT OFFICE f ROTOR PA AQH TE Richard H. Prewitt, wallingford, Pa. Application April 12, 1947, Serial No. 741,025

12 Claims. 101. 170-16011) g This invention relates to motorless aircraft. In' particular, it may be called afRotorchu'tei,

I wherein auto-rotating blades are utilized in place of a canopy for lowering aload from an aircraft to the ground, or, with minor modificatiohsxit may be utilized in towing a load from behind another aircraft, for transporting the load to a desired location for release prior to descending i to the ground. In particular, the Rotorchute described in this invention incorporates flexible blades. For compactness in storage and to minimize damage when being ejected'from an airtrifugal forces on the blades and eventually is airborne in autorotation where the lift forces are balanced by the'normal component of centrif-- ug'al forces.

In particular, the following specifications and drawings describethis invention inmore detail:

Fig lisan elevation of the invention, showing the blades rolled above the hub.

,Fig. 2 is another elevation of the invention, showing the blades rolled below the hub.

Fig. 3 is a plan view isometric and cutaway sketch of the blade, its hub attachment and a broken view of the hub.

I Fig. 4 is a view of the blade anchorv looking outboard. I Fig. 5 is asection of theIblade in an outboard region.

Fig.6 is a sectional view of the hub. Fig. 7-is' a plan view of the unit shown in Figs. 1 and 2, at reduced" scale, but with the blades outstretched. l r A,

Fig. 8 is as'ectionaljview taken along the line6''|.- v

Fig. 9 is an elevational vview of the stiffening member located internally at the inboard end of the blade."

Fig. 10 is'a sectional view of theanchors shown I inFig.

Fig. 11 is a fragmentary elevational view of Q the inboard anchor of trailing edge member l9.

' Fig. 12 is provided to illustrate diagrammatically. the relative dispositions of yieldable and/or elastic materials'which may be usedin the various partsof the blade section shown in Fig. 5. Fig. 13 shows diagrammatically, the chordwise CG of the airfoil section of the blade and the related aerodynamic forces resulting from its shape. e I

' With reference to Figs. 1 and 2; blades l are inboard portion beyond rib l3.

. 2- rolled above the hub and held in place through ripcord 44 and static line 45. Blades are firm- 1y attached to hub 2, which also carries cylindricalmember 3| Container 3 is, supported through members 4 to disc 32 which is permitted to turn within hub cylindrical member 3|. The righthand view of Figs. 1 and 2 shows the trailing edge of blade I, and the left-hand side of Figs. 1

and 2 shows the leading edges of blade 1.

Referring to Fig. 7, blades I, having leading edges 42 and trailing edges '43, turn in the direction indicated by the arrows 8. Blades' I are attached to hub 2 at 5. The attaching member 5, in combination with the straightening action of the centrifugal tension acting on the blade,

creates an effective blade hinge along the line 6'|, which may form an acute angle delta three Withthe blade longitudinal axis measured to the leading edge side of the blade, or the angle delta three may be an obtuse'a'ngle by changing the hub and direction of the line 6-1 created through .the attaching members 5, depending upon desired operational conditions more fully described hereafter. 7 f

Referring to Fig. 3, blade having leading edge 42, trailing edge 43, and tip 4|, is fabricated with chordwise stiffening rib members 9, III, II, l2, and I3. Outboard rib members 9 aresimilar, but inboard rib members ID, IL |2, and |3 are .provided with an additional aperture near the leading edge to accommodate spring member |4. Leading edge cable trailing edge stiffening-member l9, and cable orwire members I8 extendlongitudinally of the blade from'the inboard attachment fitting-22 to the blade tip 4|.

Yieldable material completes the' airfoil shape between ribs 9, III, II, |2, and I3, as well-as the This material may be of a combination cork and resin, cork and rubber, pure rubber, or other-suitable material."- Its main purpose is to provide proper external airfoil shape and to transmit the air loads to the longitudinally extending members described above, while being longitudinally lithe,

i. e. capable of being easily bent, pliant, limber,

flexible, at least spanwisely.

When the Rotorchute is in operation; i. e. ro-

tating at good speed, such as in autorotation, the

longitudinal structural members, including the leading edge cable wires or cables; I8, and

trailing edge strap l9, will be under heavy centrifugal loads, which will tend to keep them straight between rib members 9, l0, H, I! and Hi, where they are each individually fixed at these members, which maintain proper chord-' 3 wise shape. Thus, the material which is attached to said longitudinal structural members is positionally established internally and therefore the airfoil shape will not greatly deviate from its initial designed form.

As described for Fig. 7, above, the angle delta three may be altered as desired to meet the vari ous conditions which might be encountered in dilferent types of application; as, for example, deployment at high speed or deployment at low speed, or-altering the speed at which the rotor accelerates at a given deployment speed. Strap 20, an addition to the disclosure of Fig. 7, shown in more detail in Fig. 8, is provided, to create the proper angle delta three, and with suitable assortment of holes 48 in hub plate 2 the'effe'ctive angle delta three can be varied as desired. Such changes in location of strap 20 mayrequire areshaping of this member to fit the new contour. since the strap will pass-over the shaped upper surface of the blade at a different angle. Plate '22 isbolted to a mating surface 24 extending up froni'hub 2 through bolts 23. The center of gravity of'the inboard end of the blade maybe brought aft-by weight 49 to obtain desired-blade operationas described in detail hereinafter. 1

With reference to Fig. 8, strap 29 extends over the blade I and down through hub plate 2 where it isanchore'd by nuts 2i. It may be found desirable to use a different 'typeof filler material between the leading edge ofthe airfoiland the trailing edge of the airfoil, as at 21 and 28,- or between the upper section of the airfoil and the lower section of the airfoil, as between 21 and38, or 2&3 and 39 depending upon balance requirements for specific applications, and'also other considerations, such as blade efiiciency, temperature requirements, etc.

Fig. 9 is a detail elevational view of the stiffen ing springmember 14 shown in Fig. 3. Ashlu'strated, it is made up of a series of rectangular 'sectionsof springlike material, suchas spring steel, suitably bonded together to operate as a unit. It may-be noted that the inboardend carries angularly shaped or flanged members it and [6, which forms a means of anchoring the spring member l4 to-transmit its centrifugal tension to the hub.

Figje' shows the means of anchoring'the 'in- .board end of blade I. Hubmember 2- carries projection. 2 4, which-mates with fitting 22. Along the mating surface between members 22 and projection 24 suitable slots and counterbores are provided for cable l'l'," trailing edge 159 .and wire or cable members I8. In addition, a rectangular apertureis provided for springmember M, anchored in place by projections l5 and It. Like- ;wise a suitable slot is provided for trailing edge member l9, which is held in position by projection members' lS. Member "22 iss held inhplace through stud members 40 and1nuts'23.

A'sectional view of Fig. 4 i's'shown-in Fig. 10, where projecting member 24 lies 2 below cable member :I 8 and'ball anchor fitting'25and'member 22 lies above said cable -and anchor'ball. Anchor ball 25 is swfaged to cable l8 in'such manneras to transmit all of the centrifugal tension incablememberl8, asshown, and in nose cable I'L'not shown, but similarly attached to-hub projection 24 and mem-ber22. The centrifugal tension in spring" member l4 and trailing edge member I 9 is transmitted to hub projection 24 and member 22 through suitably formed pro-v "tions 21, upper, and 38, lower.

jections l5 and [6 for spring member [4 and 46 for trailing edge member [9.

Fig. 5 shows a sectional view through an outboard section of the blade. The longitudinal structural members are shown as the leading edge cable l7, cable or wire members I8 and trailing edge member I9, all of which lie su-bstantially along a straight line, so that these structural members are not greatly elongated or shortened when the blade I is rolled.

-With reference'to Fig. 12,- the'area within the blade section is divided into leading edge sec- It is proposed to employ varying materials at different sections of the blade, noted above, in order to cause the blade "to'balance properly chordwise, and toprovide desirable elastic properties for the various operations of the blade. For example,

inorder to bring the center of gravity of the blade forward, it may be desirable to utilize relatively heavy. materials, such assolid rubber, 'in the leadingedge sections. 2l -.and- 33,.and a relatively light material in the .aft sections. 28 and '39. Again'it may .be desirable to .utilize a high damping material for the upper sections '21 "and 2S, and a' re-stressed highly elastic material for portions38 and 39, .(such' distribution of materials mayextend onlyover -a.portion of the "blades, oronly in a portionlof the areas 12l,"28,'33 and/or'39); oragain. it'.may.be 'desirable'to utilize alight material for sections 27 and 28 and-'ahig'hly elasticmaterialfor' portions .38and 39, depending upon .the specific applications; i. e., deployment at .high or low speeds, and desired-rate of acceleration, yet maintaining proper chordwise balance.

Fig. 6, a sectional view of the hub-,showshub member 2, towhich is fixedly attached cylindrical member 3|, which carries internally. bearing-35 secured from vertical movement throughv projection 4'! and retainer ring 34. "Structural members 4 are fixed to disc member32 which carries axle 36 foribearing '35. Nut.' 33 secures disc member 32 to the inner part of bearing 35. Cover plate 29 is securedto hub 2 ithrough' suitable fastener 30.. V

Fig. 11 showsa detail at the inboard anchor attachment of trailing edge member l9. Anchor members '46 are securely attached i to trailing edge member [9 and. provide an anchor for same.

Fig. 13 showsthe'chordwise CG of the blade at CG located underneath the aerodynamic. center AC. The'air load'vectors'm'arked (11),". (b), and (0) represent the.tota1 airloadoperating on the blade at various angles. .ofattack; i.. e., vector (0.) represents the loading when the blade is operating at a low angle of attack. -Vector (b) represents the airload actionon lthe blade when it is operating at a normal, or greatersthan normal, angle of attack, and vector ((2) represents theairload acting on the bladewhen. it

- is operating at a high angle of attaclgpriorto stall. Thus, it may be seen that-when-the blade is operating at a high angle of attach-below the stall, a small moment iscreated about the chordwise CG of vthe- ,blade," tending --to plower the leadingedge and z raise the trailing edge. Conversely, when the blade is-operating at a low angle of attack, represented-by vector (a) there is a moment ,around-thechordwise.CG of the blade tending-to raise the leading edge and lower the trailing edge of theblade, which would have the eifect of increasingfthe anglefof'attack. It can readily'be seentha't a selected airfoil having the characteristics illustrated would,.ne'glectstrength 1members .l 1, ;s tabilizing force is created which ,tends' to keep the tip of the blade in line with'the root of the edge when air loads tending I v I a against the aforementioned resilient forces and (bl; which jpassesj directly through the ;chordwiseCGtof-the blade, which may-,befslightly aft. directly j-underneath the vof a line extending aerodynamic. center 7 AC. 1

, Inqiaddition .to the. aerodynamic stabilizing.

two centrifugal stabilizing. forcesin. operation; first, thereis that I centrifugal stabilizing force commonly known propeller design, vwhichtends to keep the chord- .iforces. taught above, there are lngotheriorcesrhave a tendency tffioat-stably Y :the-anglev of attackrepresented.bythe vector I I -wise-distributed weight of the blade. inthe. plane I of rotation; andsecondly, due to the chordwise spreading l8, and l9,:'an additional blade, as any twistingwould tend to move the a blade elements closer to the hubagainst the centrifugal forces while operating.- In order to olfset the last two stabilizing forces it maybe found desirable to place the chordwise center of gravity, aft of the position illustrated in Fig. 13, with the longitudinally disposed strength members; I], I8, and J9. lying substantially in the plane. of

.disc at the hub, or. I may choose. toset the aforementioned,longitudinally disposed strength members l'l, I8,';- and I9 at a positive angle-of attack at the hub, and the chordwise CGfurther ahead. suchadevice as described in this-invention mustbefree from destruction due to handling loads. It must start windmilling and proceed into the of the longitudinally extending a autorotation as desired forthe different conditions of operation, 1. e., deployment at low speed,

or deployment at highispeed. Likewise it must yention recites the variousmeans to accomplish the desired results. --For example, the leading- ;edgeofthe blade has greater resistance todeflection, as in rolling the blade up, then'the trailing descend with stability. The-disclosure of this, in-

of the initial center .edge, sincethe leading edge longitudinal stifiening members, including the specific stiffening member-l4, are designed to be stiffer thanthe trailing .je'dge longitudinal structuralmemb'ers, including the fiat trailing edge member'lil, 'Llkewise, the :filler material usedbetweentheribs' and attached ,to the longitudinal structural members may have greater resistanceto bending in-the leading edge portion of the blade than in the trailing edge portion of the blade. With this device, upon deployment, the. leading edge of the blade'will be forced down to a greater extent than the trailing the blade is reacted on by air forces prior 'to establishing autorotation. It may be seen thatthe airforceswill act upwardonthe blad centered at a point approximatelyhalfway be ween theleading edge andthe trailing edge and; by. maintaining greater resistance. to these I air forces atthe leading edge, the blade will tend to twist near the hub into a lower anglejof attack, thusproviding initial WindmiIling prior to establisliing autorotation. When the rotor starts to th lblade, causing the blade to become balanced a. cone p0siti0il,. depending upon the relation-., p of tending to keep theblades outstretched and the to how the blades upwind centrifugal forces.

aircraft-traveling. atlow. speed accelerate into i autorotation rapidly, and therefore, for low speed, operation, it wouldbe desirable-for the blade t.o

eil iel rt i tt ou p xim t ly. .45 nega1- the aforementioned centrifugal forces -tive angle, and for "said increase -.to a slight positive angle when auto-.

high angle of attack,

"factors existed. The

angle toprogressively rotation has been established.

When deployment occurs at high speed, is

, desired that the transfer into autorotation be delayed sufficiently to prevent excessive shock on the pilot or materialwhich is being lowered :to the ground. In this case there are two possible methods of accomplishing the desired result.

loa s One is to cause the blades to be twisted as described above'toan excessively small angle of attack, such that the windmilling' speed of the rotor would be limited; and the other method would be to cause the rotor to goto a relatively high velocity or high; load former method of delaying autorotation is automatically accomplished. by

rotation so long as the methods described above for slow speed de- .0)? the airfoil, suchas might place the airfoil CG at a distance halfway betweenthe leading edge .and trailing edge, then no moments would be created as a result of inertia loads. ments-would thenbe purely a relationshlpbetween air loads and the resistance of the blade in bending, and by placing the CG slightly aft of pressure of the air load, the twisting moments created by the bending stiffness of the blade toward the leadingv edge would be partially offset. Thus, the chordwise CG near the inboard end of the blade, as well as the chordwise position of the center of resistance to bending of the blade, each form an important turncentrifugal forces will act on the elements of t I I 970 It is desired that a Rotorchute dr pped from an part in determining the characteristics of the Rotorchute during deployment, with special reference to the rapidity at which it goes into autorotation. I

In addition to the above, itmay bedesirable .to incorporate prestretched or pre-compressed filler materials in the blade, or pre formed structural material in the blade, so disposed and 'arranged to cause the blade to deform locally under the influence of such resilient materials. Yet.

when the Rotorchute incorporating these devices goes into autorotation, with accompanying centrifugal loads, the effect of such deformingde;

efiect of the centrifugal loads tending to straighten the blade. These deforming devices may therefore be particularly effective in'the initial stages priorto attaining autorotation. Th cooking of the delta three angle-, iillus-y trated in Fig.3 and Fig. '7) has a profound-effect upon the operation of the Rotorchute. With a delta [three angle less than the blade will tend to decrease its angle of incidence as. it,

progresses into a higher coning angle, and this would have a tendency to increase the autorotational speed, which, in turn, through greater centrifugal tension, would tend to lower theconing angle of the blade. but-before autorotation, blades mounted with an acute delta three angle would have atendency to lower the blade pitch with higher coning angle,

yet at the same time the tip of thebla'demoves which would preclude ,auto- I the latter: method, where a weightvices will be greatlymmimized by the counter Initially after deployment,

forward, creating :a 'component' of wind "forces ronto the leadingedge of .the blade. The tendency of the blade to decrease its angle of inci- "dencedue to an acute delta three angle would tendto create a positive driving force toward proceeding into autorotation, and the aforementloned'component of drag force acting on the leading edge of the bladetends to create a negativedr'iving force and one which would tend to retard acceleration of the rotor.

i Conversely, a .delta three angle greater than 90' would have a tendency to go to higher pitch 'angles'with increased coning, and the blade would tend to'move aft toward the tip, thereby creating a component ofair force from trailing edge: to leading edge. The increased incidence angle-f the" blade' created by'a delta three angle greater thaii'90'would tend to retard acceleration of the "rotorpye't the component of air forces directed from trailing edge to leading edge would tend to a'cceleratethe rotor. The resulting accelerating or decelerating forces must not only take into account the relative coning angle but also the relative value of torque moment forces between the aerodynamic resistance when the air is impinging on the fiat face of the blade and the aerodynamic'resistance when the air is impinging on the blade chordwisely. By careful selection of theangle delta three, based on the principles 'taughtabove, in combinatiomwith the distribu- 'tion of blade flexibility previously discussed, it is possible to obtain the desired Rotorchute characteristics for any given application.

It is understood that this invention is not limited to the'airfoil'shapes and dimensions shown herein, and that'other shapes may be employed to attain the desired results.

' Having thus described my invention, I claim:

1. In rotary-wing aircraft, a, hub, a longitudinally lithe blade, means operatively associated with the blade to render it stiff chordwisely and flexible longitudinally, said blade having a longitudinalaxis, a bending edge strap straddling said blade, and complemental means on the strap and hub to hold the strap rigidly in a, selected one of a plurality of positions in overlying relation to the blade, to establish a selected line of flexure of the 'blade angular relative to the longitudinal axis: thereof establishingv the delta three angle ofthe blade and thus predetermining the operating characteristics of the blade when first deployed.

2. In a rotary wing aircraft, a, longitudinally lithe blade comprising a flexible structural member extending longitudinally of the blade, a plurality of longitudinally spaced chordwisely extending structural members eachof substantial stiffness mounted on the said flexible member, and a supplemental resilient device located in said blade closer to the leading edge than to the trailing edge and of generally progressive variation' in stiffness in its length decreasing'from the rootof' the blade for renderingitheblade resilientlystiifer toward the leading edge than toward the trailing edge so as to enhance deployment and wlndmilling without precluding coiling of the blade. 3'."In a rotary wing lithe bla'decomprising a flexible structural memberiiextending longitudinally of the blade, 2. plurality of longitudinallyspaced chordwisely extending structuralsmembers each of substantial stifiness. mounted on: the. said flexible member, andxa resilient "member. in. the forward portion ori'the zbladeicomprisinga' resili'ent device anstructural 7 elementthe blade aerodynamically chordwisely asymmetrical thereof, said-element being stiifer adjacent the root of the blade than at its spanwise chaired 'in the blade root andterminaung spanwisely short of the full blade-span for rende'ring the leading edge of the blade resiliently stiffer againstc'oning than the trailing edge thereof without precluding coiling of the blade sothat upon deployment the blade can assume a windmilling anglefrom reaction "with the air. through :which it moves as a preliminary to 1 autorotation.

f 4. ma rotary wing aircraft, a longitudinally l'ithe"blade-arrangedfor effective coiling, a' fiexible i structural f element extending longitudinally of the bladeraerod ynamically chordwisely. asymmetrical thereof, said.element being stiffer-adjalcent tothe root of the-blade thanat its sp'anwise termination insaid blade,-whereby upon' deployment from its effectively coiled attitudethe-blade is urged into windmill angles 1 of 1 attack.

5. In 1 a, rotary Wing aircraft, a longitudinally lithe bladehaving .a longitudinal axis, a resilient extending longitudinally'of termination in said blade, a hub, "said blade mounted on the hub, and means mounted on said hub and overlying the blade for establishing a line ofefiexure of the blade relative to said hub rat a predetermined acute angle to saidlongitudinal axis thereof, saidstructural element and said-angle of fiexure cooperatingto establish the starting torque and operating characteristics of the rotor.

. 6. In a rotary wing aircraft, a longitudinally lithe blade-having a longitudinal axis, a'hub; said blademounted on the hub, meansmounted on said hub and engaging the-upper surface of the blade to constrict theblade between the hub'and said means, said means having 'abendingedge forming an angle with said longitudinal blade axisabout which edge said blade can bend in the rotative functions of the hub and blade establishinga selected line of flexure of the blade relative to said hub at a predetermined acute angle to said longitudinal axis thereof for predeterminedlyv establishing the starting torque and operating characteristics of the rotor, and'means engaging said hub and' said bending'edge means in a selected angular position relative to "said longitudinal blade axis, and means on" said :hub for mountingsaid bending edge means in another selected angular position relativeto' the longitudinal axis of said blade to vary; the-line of fiexure of the blade ,to change the operating characteristics-of-the rotor.

7. 'In rotary wing aircraft, a'flexible blade,a hub, 'means'attaching the root of the blade tothe hub with the latter means for establishing the delta threeangle'of the bladecomprising a clamp overlying the blade hub and clamp aircraft, a, longitudinally I porating a first anda second'material rials being differentially pre-stressedanddis posed in relative eifec'tive contiguity, the matepartially overlying the hub,

rials and stressing causing inherent local deformation of the blade. l

9. Rotary wing aircraft as claimed in claim 8 in which the first and second materials are both in the upper portion of theblade. 10. Rotary wing aircraft as claimed in claim 8 in which the first and second materials are both in the lower portion of the blade.

11. Rotary wing aircraft as claimed'in claim 8 in which the first and secondmaterials are re- 10 spectively in the entering and trailing edges of the blade.

- 12. In rotary wing aircraft, a blade formed of multiple structural elements and being longitu- I dinally lithe and susceptible to coiling, uncoiling, windmilling' and autorotation, said blade incorporating a first and second and a third and fourth material, in respective pairs, said materials of each pair being of respectively different elastic characteristics, said materials of each pair being differentially prestressed and disposed in mutual 10 relative efiective contiguity,

- the blade. v

RICHARD H PREWITT.

REFERENCES CITED The following references are of record in' the file of this patent:

UNITED STATES PATENTS Number Name Date I ,226,078 Pescara Dec. 31, 1940 2,234,319 Preston Mar. 11, 1941 2,330,803 Andrews Oct. 5, 1943 2,404,678 Wuensch July 23, 1946 FOREIGN PATENTS Number .v Country Date 399,607 Great Britain Oct. 12 1933 660,793 Germany June 2, 1938' 'j. 800,738

, France May 11, 1936 the materials and stressing causing inherent local deformation of 

